/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.hydraql.benchmark.core;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.util.Iterator;

/**
 * YCSB-specific buffer class. ByteIterators are designed to support efficient field generation, and
 * to allow backend drivers that can stream fields (instead of materializing them in RAM) to do so.
 * <p>
 * YCSB originially used String objects to represent field values. This led to two performance
 * issues.
 * </p>
 * <p>
 * First, it leads to unnecessary conversions between UTF-16 and UTF-8, both during field
 * generation, and when passing data to byte-based backend drivers.
 * </p>
 * <p>
 * Second, Java strings are represented internally using UTF-16, and are built by appending to a
 * growable array type (StringBuilder or StringBuffer), then calling a toString() method. This leads
 * to a 4x memory overhead as field values are being built, which prevented YCSB from driving large
 * object stores.
 * </p>
 * The StringByteIterator class contains a number of convenience methods for backend drivers that
 * convert between Map&lt;String,String&gt; and Map&lt;String,ByteBuffer&gt;.
 */
public abstract class ByteIterator implements Iterator<Byte> {

  @Override
  public abstract boolean hasNext();

  @Override
  public Byte next() {
    throw new UnsupportedOperationException();
  }

  public abstract byte nextByte();

  /** @return byte offset immediately after the last valid byte */
  public int nextBuf(byte[] buf, int bufOff) {
    int sz = bufOff;
    while (sz < buf.length && hasNext()) {
      buf[sz] = nextByte();
      sz++;
    }
    return sz;
  }

  public abstract long bytesLeft();

  @Override
  public void remove() {
    throw new UnsupportedOperationException();
  }

  /**
   * Resets the iterator so that it can be consumed again. Not all implementations support this
   * call.
   * @throws UnsupportedOperationException if the implementation hasn't implemented the method.
   */
  public void reset() {
    throw new UnsupportedOperationException();
  }

  /** Consumes remaining contents of this object, and returns them as a string. */
  public String toString() {
    Charset cset = Charset.forName("UTF-8");
    CharBuffer cb = cset.decode(ByteBuffer.wrap(this.toArray()));
    return cb.toString();
  }

  /** Consumes remaining contents of this object, and returns them as a byte array. */
  public byte[] toArray() {
    long left = bytesLeft();
    if (left != (int) left) {
      throw new ArrayIndexOutOfBoundsException("Too much data to fit in one array!");
    }
    byte[] ret = new byte[(int) left];
    for (int i = 0; i < ret.length; i++) {
      ret[i] = nextByte();
    }
    return ret;
  }

}
